?program to replace text in text files

Hi, Does anyone know of a (command line) program in SuSE that allows you to replace all occurences of a certain string in a text (CSV) file with another? I have a (huge) file which contains Matlab style 'NaN' for missing data and I need to make it Gauss readable by replacing all the 'NaN' with the symbol '.'. It's too big to be loaded into an editor or excel etc. thanks, j. __________________________________ Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month! http://sbc.yahoo.com